1,1

Next term of the sequence is greater than 10^9. All semiprimes of the form 4*10^m-3 are in the sequence - the proof is easy. For m=3,6,11,12,13,15,16,18,19,24,38,56,60,... 4*10^m-3 is semiprime. Is it true that, 3 is the only prime term in the sequence?

phi(168632373)+sigma(168632373)=87744384+285492480=373236861+3= reversal(168632373)+3, so 168632373 is in the sequence.

Do[If[DivisorSigma[1, n]+EulerPhi@n==FromDigits@Reverse@IntegerDigits@n+ 3, Print[n]], {n, 500000000}]

Cf. A136545, A136546.

Adjacent sequences: A136541 A136542 A136543 this_sequence A136545 A136546 A136547

Sequence in context: A003831 A089895 A116213 this_sequence A024048 A094319 A003166

base,more,nonn

Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 20 2008